Five years ago, C.K. Prahalad published a book titled, The Fortune at the Bottom of the Pyramid , in which he argues that multinational companies not only can make money selling to the world’s poorest, but also that undertaking such efforts is necessary as a way to close the growing gap between rich and poor countries. Key to his argument for targeting the world’s poorest is the sheer size of that market — an estimated four billion people. How has Prahalad’s book — a revised, fifth-anniversary edition of which has just been published — affected the behavior of companies and the well-being of consumers in the years since its publication?…